Two dimensional arrays of visible light emitting devices, such as light emitting diodes (LEDs), are becoming very useful in displays for portable electronic devices, such as telephones, cellular telephones, two-way radios, pagers, etc. Generally, these two dimensional arrays include large numbers of light emitting devices, from 5000 to 80,000 or more, with a specific example being 144 rows by 240 columns.
One important factor in the quality of an image viewed on a given display, whether real or virtual, is the fill factor of the pixels within the emitting area. A high fill factor is desirable to obtain high quality images. For CRTs, the emission profiles of adjacent pixels actually overlap giving effective fill factors greater than unity, and producing a very smooth (not grainy) image. With matrix LED displays, however, it is not possible to achieve unity fill factors since there needs to be isolation between pixels. In addition, since conventional row/column matrix addressing schemes use metal row and column interconnects, there needs to be room for the column and row interconnect busses to pass through the pixel and to make contact to each electrode of the diode making up the pixel. For the columns, this interconnect component turns out to be the major component in the space required between pixels because of the minimum line width and alignment tolerances associated with this interconnect bus/contact processing.
In U.S. Pat. No. 5,483,085, entitled "Electro-optic Integrated Circuit and Method of Fabrication", issued Jan. 9, 1996, and assigned to the same assignee, a method of fabricating LED arrays is disclosed utilizing implant technology for isolation and separation. As can be seen in the figures of the '085 Patent, one minimum dimension is needed for isolation, another for the column bus/cathode contact, and two alignment tolerances for placement of the metal. Generally, utilizing the present semiconductor fabrication techniques, 2 micron minimum line widths, spaces and alignment tolerances together with a 10 micron emission square for each diode give a minimum linear fill factor of 0.5 or an area fill factor of (0.5).sup.2 =0.25. The images produced by this display can be somewhat grainy as a result of this relatively low fill factor.
Another problem that is prevalent in the industry at the present time is the limitation on colors of LEDs that are available and/or practically manufacturable. When producing a full color display, for example, the three basic colors, red, green and blue, must be available. In many instances the colors generated by LEDs fabricated on one material system are far from the primary colors, resulting in less than desirable displays.
Accordingly, it is highly desirable to provide light emitting device arrays which overcome these problems.
It is a purpose of the present invention to provide new and improved light emitting device arrays.
It is another purpose of the present invention to provide new and improved light emitting device arrays with a substantially improved fill factor.
It is another purpose of the present invention to provide new and improved light emitting device arrays which require the same semiconductor chip area as prior arrays, for larger numbers of light emitting devices.
It is still another purpose of the present invention to provide new and improved light emitting device arrays with substantially improved color.
It is a further purpose of the present invention to provide a new and improved method of fabricating light emitting device arrays.
It is a still further purpose of the present invention to provide a new and improved method of fabricating light emitting device arrays which is simpler and more efficient than prior methods and which is easily adaptable to high production levels.